Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Sodium Metabisulfite (Disodium Disulfite)
Downloaded by CORNELL UNIV on May 31, 2017 | http://pubs.acs.org Publication Date (Web): February 28, 2017 | doi: 10.1021/acsreagents.4353
Part 4, Monographs for Reagent Chemicals: General Descriptions, Specifications, and Tests eISBN: 9780841230460 Tom Tyner Chair, ACS Committee on Analytical Reagents James Francis Secretary, ACS Committee on Analytical Reagents
ABSTRACT This monograph for Sodium Metabisulfite provides, in addition to common physical constants, a general description including typical appearance, applications, and aqueous solubility. The monograph also details the following specifications and corresponding tests for verifying that a substance meets ACS Reagent Grade specifications including: Assay, Insoluble Matter, Chloride, Thiosulfate, Heavy Metals, and Iron.
Na2S2O5
Formula Wt 190.11
CAS No. 7681-57-4
GENERAL DESCRIPTION Typical appearance . . . . . . . . . . . . . . . . . . . white solid Applications . . . . . . . . . . . . . . . . . . . . . . . . reducing agent Aqueous solubility . . . . . . . . . . . . . . . . . . . . 64 g in 100 mL at 20 °C
SPECIFICATIONS Assay . . . . . . . . . . . . . . . . . . . . . . . . . . . . ≥97.0% Na2S2O5 Maximum Allowable Insoluble matter . . . . . . . . . . . . . . . . . . . . . 0.005% Chloride (Cl) . . . . . . . . . . . . . . . . . . . . . . . 0.05% Thiosulfate (S2O3) . . . . . . . . . . . . . . . . . . . . 0.05% Heavy metals (as Pb) . . . . . . . . . . . . . . . . . . 0.001% Iron (Fe) . . . . . . . . . . . . . . . . . . . . . . . . . . 0.002%
© 2017 American Chemical Society
A
ACS Reagent Chemicals ACS Reagent Chemicals; American Chemical Society: Washington, DC, 2017.
DOI:10.1021/acsreagents.4353 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
TESTS Assay (By titration of reductive capacity). Weigh accurately about 0.45 g, and add to a mixture of 100.0 mL of 0.1 N iodine volumetric solution and 5 mL of 10% hydrochloric acid solution. Swirl gently until the sample is dissolved completely. Titrate the excess of iodine with 0.1 N sodium thiosulfate volumetric solution, adding 3 mL of starch indicator solution near the end of the titration. One milliliter of 0.1 N iodine corresponds to 0.004753 g of Na2S2O5.
Downloaded by CORNELL UNIV on May 31, 2017 | http://pubs.acs.org Publication Date (Web): February 28, 2017 | doi: 10.1021/acsreagents.4353
Insoluble Matter [Part 2: Gravimetric Methods; Insoluble Matter]. Use 20 g dissolved in 200 mL of water.
Chloride Dissolve 1.0 g in 10 mL of water, filter if necessary through a small chloride-free filter, and add 6 mL of 30% hydrogen peroxide. Add 1 N sodium hydroxide volumetric solution until the solution is slightly alkaline to phenolphthalein, and dilute with water to 100 mL. Dilute 2.0 mL of this solution with water to 20 mL, and add 1 mL of nitric acid and 1 mL of silver nitrate reagent solution. Any turbidity should not exceed that produced by 0.01 mg of chloride ion (Cl) in an equal volume of solution containing the quantities of reagents used in the test.
Thiosulfate In a 50 mL beaker, dissolve 2.20 g of the sample in 30 mL of water. Simultaneously, for the control solution, dissolve 1.10 g of the sample in 30 mL of water, add 0.50 mL of 0.01 N sodium thiosulfate solution (freshly made from 0.1 N sodium thiosulfate volumetric solution). To both solutions, add 1.0 mL of 0.1 N silver nitrate and 5.0 mL of sulfuric acid (1:1). Mix each solution, and allow to stand for 5 min. The color of the sample solution should not exceed the brownish color of the control solution.
Heavy Metals [Part 2: Colorimetry and Turbidimetry; Heavy Metals (as Lead); Procedure for Heavy Metals, Method 1]. Dissolve 3.0 g in 25 mL of dilute hydrochloric acid (2:3), and evaporate to dryness on a hot plate (~100 °C). Add 5 mL of hydrochloric acid, and again evaporate to dryness. Dissolve the residue in 20 mL of water, and dilute with water to 25 mL. For the control, add 0.02 mg of lead to 1.0 g of sample, and treat exactly as the 3.0 g of sample.
Iron [Part 2: Colorimetry and Turbidimetry; Iron; Procedure for Iron, Method 1 (Ammonium Thiocyanate)]. Dissolve 0.50 g in 14 mL of dilute hydrochloric acid (2:5), and evaporate on a hot plate (=100 °C) to dryness. Dissolve the residue in 7 mL of dilute hydrochloric acid (2:5), and again evaporate to dryness. Dissolve the residue in 2 mL of hydrochloric acid, dilute with water to 50 mL, and use the solution without further acidification.
© 2017 American Chemical Society
B
ACS Reagent Chemicals ACS Reagent Chemicals; American Chemical Society: Washington, DC, 2017.
DOI:10.1021/acsreagents.4353 ACS Reagent Chemicals, Part 4
